Process of crushing and grinding calcium carbid.



i "n era" 1 PATENT orrron WALTER S. LANDIS, OF NIAGARA FALLS, ONTARIO, CANADA, ASSIGNOR T0 AMERICAN CYANAMID COMPANY, OF NASHVILLE, TENNESSEE, A CORPORATION OF MAINE.

PDIOCESS OF CRUSHING AND GRINDING CALCIUM CARBID.

No Drawing.

To all whom it may c0nce7'n Be it known that I, WALTER S. LANDIS, a citizen of the United States, residing at Niagara Falls, in the Province of Ontario and Dominion of Canada, have invented certain new and useful Improvements in Processes of Crushing and Grinding Calcium Carbid; and I do hereby declare the following to be a full, clear, and exact description of the in vention, such as will enable others skilled in the art to which it appertains to make and usethe same.

This invention relates to a process for crushing and grinding calcium carbid, preparatory to making calcium cyanamid or Ior other purposes, and has for its object to carry out the above operations in a better, safer, and more expeditious manner than. has heretofore been proposed.

To these ends the invention consists in the .novel operations or steps and combinations of steps constituting my process as are more fully hereinafter disclosed and particularly pointed out in the claims.

In order that my invention may be clearly ing reactions:

The amount of such slaln'ng and the rate at which it takes place depends on the m'oisture content ofthe air, the air circulation and also on the size of the individual particles of carbid exposed, or in other words the total surface of carbid exposed to the action of the air.

The acetylene evolved mixes with the air, and if ventilation is not most carefully provided, it may accumulate to such an extent as to form an explosive mixture, which is easily ignited by the sparks incident to crushing and grinding such hard material as calcium carbid. It, therefore, follows that not only is grinding and crushing the carbid in air accompanied by a great loss of valuable material, but is also subject to the risk and danger accompanying violent acetylene-air explosions. Further, as the grind ing progresses to the extremes of producing a product of a fineness of 100 mesh and even Specification of Letters Patent.

Patented June 16, 1914.

Application filed June 7, 1913. Serial No. 772,398.

finer, this action of the air and consequent dangers become more and more pronounced.

For the extreme fine grinding required in the cyanamid industry, it was early recognized that it was very undesirable to conduct this operation in the air, particularly on warm humid days, for the weathering of the fine carbid was so great as to entail prohibitive losses in the finished product, and in addition the slaked product resulting would clog the mills so as to make an almost continuous cleaning necessary. To remedy this it has been proposed to fill the crushing and grinding machinery with dry air, but it was found commercially very difficult to obtain an atmosphere of pure or absolutely dry air, forthere is always some acetylene generated due to the slow weathering of the carbid, with the consequent liability of the formation of the explosive acetylene air mixtures, as above explained.

In fact, actual experience has shown that not only have the above objections and losses been encountered, but at least one fatal explosion has occurred due to the acetylene being liberated from the carbid.

I obviate all of the above disadvantages by feeding dried nitrogen gas to the grinding machinery, as well as to the conveying, elevating and storage equipment which handles the ground carbid.

The cyanamid industry calls for enormous quantities of extremely pure nitrogen gas, which often analyses above 99.8 per cent. nitrogen and which often does not contain an average over a month as much as one milligram of water vapor to a cubic foot. It is this gas which I use, and the importance of the use of this particular gas over the use of any ordinary and less pure nitrogen gas that is commercially available will be understood when it is said-:Ordinary nitrogen gas which can be obtained commercially from other sources, always contains suflicient oxygen and other impurities as to cause a certain amount of weathering of the carbid; and the losses in actual practice on large scale grindings due to weathering have often amounted to as much as six per In addition to the above the efiicient nitrification of the carbid requires a fresh surface to be exposed to the nitrogen, and the weathering of said carbid in the past has interfered to a greater or less extent with the efliciency of the nitrification. In other words actual experience has shown that the above weathering and losses incident thereto have been very greatly reduced, both in connection with the grinding machinery, as well as in connection with the elevating and storage equipment, and no explosions at all have occurred since these operations have beencarried out in an atmosphere of substantially pure nitrogen.

'I find it preferable to keep a circulation of nitrogen through the grinding, conveying, elevating and storage machinery, and tokeep the nitrogen pressure above that of the atmosphere throughout the system so that no air leakage will occur. This enables me to keep the acetylene contents of the atmospheres present in the system below five per cent. and even below three per cent. in some cases, which with the nitrogen present obviates all danger of explosions.

Further, as above explained, the weathering itself and the severe losses incident thereto, especially in fine grinding is reduced to considerably below one half, and sometimes below one fourth ofiwhat they would be without the nitrogen atmosphere.

Any suitable and well known means may be employed for carrying out my invention, all that is necessary being an inclosure for the machinery to prevent a too rapid waste of the inert gas or gases employed. In

.some cases, a tight room in which the machinery is located will be suflicient.

What I claim is 1. The process of preventing explosions as well as lessening the weathering of calcium carbid and the losses incident thereto during the process of grinding said carbid which consists in carrying out the grinding opera tions in an atmosphere of substantially chemically pure nitrogen, substantially as described.

2. The process of preventing explosions as well as lessening the weathering of calcium carbid and the losses incident thereto during the steps of crushing. grinding, conveying and storing said carbid which consistsis carrying out said steps in an atmosphere of substantially chemically pure nitrogen, substantially as described.

3. The process of preventing explosions as well as lessening the weathering of calcium carbid and the losses incident thereto during the operations of reducing said carbid to a state of fine division and of storing the same, which consists in carrying out said operations in a stream of substantially chemically pure nitrogen gas, maintained at a pressure above that of the atmosphere, subs stanti-ally as described. I

In testimony whereof I aflix my signature,

in presence of two witnesses.

W'ALTER S. LANDIS.

Witnesses:

O. S. MALLAM, S. HANNA. 

